OPTOMETRY RESEARCH PAPER. Visual performance comparison between contact lens-based pinhole and simultaneous vision contact lenses

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1 C L I N I C A L A N D E X P E R I M E N T A L OPTOMETRY RESEARCH PAPER Visual performance comparison between contact lens-based pinhole and simultaneous vision contact lenses Clin Exp Optom 2013; 96: Santiago García-Lázaro PhD César Albarrán-Diego MSc Teresa Ferrer-Blasco PhD Hema Radhakrishnan PhD Robert Montés-Micó PhD Optometry Research Group, Optics Department, University of Valencia, Valencia, Spain Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom santiago.garcia-lazaro@uv.es Submitted: 7 December 2011 Revised: 29 December 2011 Accepted for publication: 29 April 2012 DOI: /j x Background: The aim was to evaluate the visual performance provided with a contact lens-based pinhole design against a simultaneous vision multifocal contact lens. Methods: In a cross-over study at the University of Valencia, 22 presbyopic patients were evaluated using an artificial pupil fitted on the non-dominant eye and the simultaneous vision PureVision Multifocal contact lenses. After one month of contact lens wear, binocular distance visual acuity (BDVA), binocular near visual acuity (BNVA), defocus curve, binocular distance contrast sensitivity, binocular near contrast sensitivity, and stereoacuity were measured, under photopic conditions (85 cd/m 2 ). In addition, binocular distance visual acuity and binocular distance contrast sensitivity were examined under mesopic conditions (5 cd/m 2 ). Results: Mean binocular distance visual acuity for pinhole and PureVision Multifocal were and logmar under photopic conditions and and logmar for binocular near visual acuity under mesopic conditions, respectively. No statistically significant differences were found between both types of lenses at distance for both lighting levels and intermediate distances (p > 0.05). There was a significant difference at near vision under photopic conditions (p = 0.03). Binocular distance contrast sensitivity revealed statistically significant differences between the pinhole system and PureVision Multifocal for six and 12 cpd (cycles per degree) spatial frequencies at the two luminance levels, while for near vision, differences were also significant for 18 cpd. Stereoacuity was better with PureVision Multifocal ( seconds of arc) compared with the pinhole lens ( seconds of arc, p = 4). Conclusion: Pinhole and PureVision Multifocal contact lenses provide good binocular vision for distance and functional intermediate vision. Although it was better with the PureVision Multifocal, near vision was not satisfactory for either of the two contact lens options. Key words: bifocals contact lenses, contact lenses, presbyopia, stereopsis The age-dependent loss of the ability to accommodate, named presbyopia, is primarily attributed to a decrease in lens elasticity. 1 Other possible causal factors for presbyopia include the increase in equatorial diameter of the lens, loss of elasticity of Bruch s membrane and reduced mobility of the ciliary muscle. 2 Presbyopia usually begins between ages 38 and 45 and the prevalence is virtually 100 per cent by ages 50 to 52 years. 3 Many presbyopic patients believe the loss of accommoda- 46 Clinical and Experimental Optometry 2012 Optometrists Association Australia

2 tion represents a considerable decrease in their quality of life. 4 Optical solutions to improve near vision in presbyopic patients can be classified as non-surgical or surgical. Among the non-surgical methods, the standouts are bifocal and progressive power ophthalmic lenses and multifocal contact lenses. Currently, there are two options for contact lens correction of presbyopia, namely, monovision and multifocal contact lenses. In monovision, the dominant eye is corrected for distant vision and the non-dominant eye for near. Numerous soft multifocal contact lens designs have been introduced recently. Most use the concept of simultaneous vision, that is, the contact lens has multiple powers positioned within the pupillary area at the same time with near-centre aspheric geometry, distance-centre aspheric geometry or multi-concentric surface with different rings for distance and near vision. A recent approach using an artificial pupil in a contact lens has been developed to correct presbyopia. Small pupils have long been known to increase the focal range over which monocular visual acuity and contrast sensitivity are maintained at reasonable levels. 5 The contact lens based artificial pupil used in this study was fitted monocularly following the protocol for corneal pinhole inlays implanted surgically. The AcuFocus ACI 7000PDT intracorneal inlay (AcuFocus, Inc, Irvine, CA, USA), commercially known as Kamra TM, involves the use of a 3.8 mm opaque disc with a 1.6 mm pinhole designed for monocular insertion under a LASIK flap or deep pocket incision. After flap creation in the non-dominant eye with a microkeratome or a femtosecond laser, the Kamra TM intracorneal inlay is placed halfway between the centre of the pupil and vertex normal. The dominant eye remains untreated in the Kamra inlay system. Four studies have analysed visual acuity after the implantation of this system for presbyopia correction. 6 9 Overall, these studies demonstrated an improvement in vision at distance and near with the pinhole system. It is interesting to analyse the possible benefits of contact lens-based pinhole on visual acuity and depth-of-focus for presbyopic correction and to compare them with currently marketed contact lenses. Thus, the objective of this study was to assess and compare the visual performance of patients fitted bilaterally with the contact lens-based artificial pupils and the PureVision Multifocal contact lenses by using visual acuity, defocus curve, contrast sensitivity and stereoacuity measurements. METHODS Figure 1. Artificial pupil design fitted in the present study. There is a 1.6 mm central aperture in a 8.0 mm diameter opaque zone. The tenets of the Declaration of Helsinki were followed in this study. Informed consent was obtained from all patients after the nature and possible consequences of the study had been explained. This study was approved by the institutional review board. Patients and lenses Twenty-two presbyopic patients (five men and 17 women), with ages ranging from 50 to 64 years ( years) participated in this cross-over randomised study. Inclusion criteria were age between 45 and 65 years, emmetropia (cycloplegic spherical equivalent up to 0.25 D and astigmatism up to 0.50 D) and monocular distance visual acuity of 6/6 or better with normal binocularity. Exclusion criteria included subjects with photopic (85 cd/m 2 ) distance pupil size of at least 4.0 mm, anterior segment pathology, previous intraocular or corneal surgery, cataracts, corneal abnormalities (including endothelial dystrophy, guttata, recurrent corneal erosion, et cetera), history of chronic dry eye, macular degeneration, retinal detachment or any other fundus pathology. Patients were randomly fitted with the pinhole or PureVision Multifocal (Bausch & Lomb, Rochester, NY, USA) contact lenses for the first month. After one month of wear, patients returned to be refitted with the other lens. Pinhole contact lenses were manufactured from balafilcon A (water content of 36 per cent), with two base curve radii (8.40 and 8.80 mm) and a mm lens diameter. Lens design consisted of a 1.6 mm central aperture in an 8.0 mm diameter opaque zone (Figure 1). The PureVision Multifocal is a simultaneous vision contact lens with an aspheric front surface and a back surface (base curve radii of 8.6 mm) centre-near design, with a total lens diameter of 14.0 mm (balafilcon A). The Pure- Vision Multifocal contact lens is available in both low and high addition lenses, with the former catering for near addi- Clinical and Experimental Optometry 2012 Optometrists Association Australia 47

3 tions of up to D and the latter for near additions of D or greater. In our study, only high addition lenses were used. Measurements After one month of full-time contact lens wear, binocular distance visual acuity (BDVA), binocular near visual acuity (BNVA), defocus curve, binocular distance contrast sensitivity, binocular near contrast sensitivity and stereoacuity were measured, under photopic conditions (85 cd/m 2 ). In addition, BDVA and binocular distance contrast sensitivity were examined under mesopic conditions (5 cd/m 2 ). Binocular distance visual acuity was measured using the Early Treatment Diabetic Retinopathy Study (ETDRS) high-contrast logmar chart with the Functional Vision Analyser (FVA, Stereo Optical Company Inc, Chicago, IL, USA) and BNVA were determined by means of the Precision Vision Logarithmic Visual Acuity Chart 2000 New ETDRS at 40 cm. To generate defocus curves, binocular visual acuity was measured with the ETDRS high-contrast logmar chart at four metres using a variety of lens powers in a phoropter. Patients were defocused to D spherical from manifest refraction values and logmar acuity was then recorded. Positive spherical power was progressively reduced in 0.50 D steps and logmar acuity recorded after every step until reaching manifest refraction values. At this time, negative spherical power was progressively added in 0.50 D steps and logmar acuity was recorded after every step until D. Binocular distance and near contrast sensitivity were measured using the VCTS test (Vistech Consultants Inc, Los Angeles, CA, USA) and stereoacuity was determined with the Howard Dolman system The near measurements were made at a distance of 40 cm. Data analysis Data analysis was carried out using SPSS for Windows version 12.0 (SPSS Inc., Chicago, IL, USA). Normality was checked by the Shapiro Wilk test and a pairedsample t-test and analysis of variance (ANOVA) were performed to compare outcomes between lenses. Differences were considered to be statistically significant when the p-value was RESULTS Age (years) Mean SD Range 50 to 64 Sex Female 17 Male 5 Eye with pinhole contact lens (%) Right 20 Left 80 Spherical equivalent refractive (D) Mean SD Range to Keratometry (D) Mean SD Range to Distance pupil diameter for 85 cd/m 2 (mm) Mean SD Range 3.40 to 3.80 Near pupil diameter for 85 cd/m 2 (mm) Mean SD Range 2.90 to 3.50 Distance pupil diameter for 5 cd/m 2 (mm) Mean SD Range 4.19 to 4.67 Near pupil diameter for 5 cd/m 2 (mm) Mean SD 4.07 Range 3.76 to 4.28 Table 1. Patient demographics (n = 22) Table 1 shows patient demographics. Spherical equivalent data passed the normality test (W = 0.98; p = 0.64). Mean spherical equivalent refractive error was D (range: to D), and mean near spectacle addition (minimum spectacle addition to reach 0.0 logmar) was D (range: to 3.00 D). Interpupillary distance was also measured for the calculation of near stereoacuity using the Howard Dolman system showing a mean value of mm, ranging from 59 to 67 mm. Visual acuity Table 2 summarises all mean visual acuity outcomes for distance and near vision for the pinhole and PureVision Multifocal contact lenses. Visual acuity data passed the normality test, both for far (photopic: W = 0.98, p = 0.84 and mesopic: W = 0.96, p = 0.51) and near (W = 0.99, p = 0.96) vision. No statistically significant differences were found between the two types of lenses at distance under either lighting conditions but there was a significant difference at near vision (p < 0.05). 48 Clinical and Experimental Optometry 2012 Optometrists Association Australia

4 Binocular near visual acuity was slightly worse with the pinhole contact lens compared with the PureVision Multifocal contact lens. Defocus curve Figure 2 shows the mean binocular visual acuity measurements as a function of defocus for pinhole and PureVision Multifocal contact lenses. The defocus curve provided one peak of maximum vision Artificial pupil PureVision Multifocal p-value logmar BDVA Photopic to to logmar BDVA Mesopic to to 0.03 logmar BNVA Photopic to 0.25 to BDVA: binocular distance visual acuity, BNVA: binocular near visual acuity. p > 0.05 p > 0.05 Table 2. Outcomes of visual acuity (logmar) for distance and near for artificial pupil design and PureVision Multifocal contact lens. In each case the mean and standard deviation of all subjects is given, together with the range of individual values. LogMAR visual acuity Defocus (D) PureVision Multifocal Artificial pupil Distance (cm) Figure 2. Defocus curve for the artificial pupil design and the PureVision Multifocal contact lens. The y-axis shows visual acuity (left, logmar and right, decimal Snellen) and the x-axis shows vergence (top in dioptres and bottom in cm) corresponding to D (distance vision). Statistical analysis showed no significant differences in BDVA between systems (p > 0.05) and a worsening when negative lenses were introduced from vergence of D. For the D lens case, binocular logmar acuity was better with the Pure- Vision Multifocal contact lens. The defocus curve did not show a significant difference between corrections of presbyopia for intermediate distances Decimal visual acuity (lens powers from - to - D, corresponding to optical distances between 50 cm and 100 cm, p > 0.05); however, statistical analysis showed significantly better visual acuity with the PureVision Multifocal at the D vergence (40 cm, p < 0.05). Visual acuities for negative values of defocus were significantly better with the PureVision Multifocal contact lens in the range between and D (from 25 cm to 33 cm, p < 0.05). Contrast sensitivity Binocular contrast sensitivity testing showed no statistically significant differences between both systems at lower spatial frequencies (1.5 and 3.0 cycles per degree, p > 0.05) for either distance or near or for the luminance levels (Figure 3). Binocular distance contrast sensitivity revealed statistically significant differences between pinhole and Pure- Vision Multifocal for six and 12 cycles per degree (p < 0.05), with contrast sensitivity being worse with the pinhole contact lens, at the two luminance levels. Values for binocular contrast sensitivity were lower for mesopic conditions, particularly at higher spatial frequencies. Binocular near contrast sensitivity under photopic conditions tended to become worse with increased frequency with the pinhole contact lens at six, 12 and 18 cycles per degree compared to PureVision Multifocal contact lenses (p < 0.05). Near stereoacuity A statistically significant difference was found between the two presbyopic solutions. The mean values of stereoacuity obtained with the pinhole contact lens ( seconds of arc) were worse than those obtained with the Pure- Vision Multifocal contact lens ( seconds of arc, p = 4). DISCUSSION This study compared the performance of a contact lens-based artificial pupil and a PureVision Multifocal contact lens by measuring visual acuity, contrast sensitivity and stereoacuity under different lighting conditions. Pinhole systems have the Clinical and Experimental Optometry 2012 Optometrists Association Australia 49

5 Log contrast sensitivity capacity to provide functional near and intermediate vision by increasing the depth-of-field of the eye. Depth-of-field is defined as the distance in front of and beyond the object of regard that appears to be in focus. Depth-of-field increases by reducing the aperture size; 13 however, there is a limit to how much the pupil size can be reduced. As the pupil size decreases, the amount of light transmitted is also reduced and diffraction increases, thus reducing visual acuity. Computer modelling suggests that an aperture of 1.6 mm provides sufficient depth-of-field, while minimising the impact of diffraction on visual acuity. 6 In a recent study, García- Lázaro and colleagues 14 compared the visual performance of different contact lens-based pinholes to improve depth-of- Spatial frequency (cpd) Log contrast sensitivity Distance photopic Pinhole PV Log contrast sensitivity Spatial frequency (cpd) Near photopic Spatial frequency (cpd) Distance mesopic Figure 3. Top-left, binocular photopic (85 cd/m 2 ) and top-right, binocular mesopic (5 cd/m 2 ) log contrast sensitivity functions for distance for the pinhole design and the PureVision Multifocal contact lens. Bottom, binocular photopic (85 cd/m 2 ) log contrast sensitivity function for near for the pinhole design and the PureVision Multifocal contact lens. The y-axis shows log contrast sensitivity and the x-axis spatial frequencies, in cycles per degree (cpd). means statistically significant differences between both systems. Pinhole PV Pinhole PV field of presbyopic patients and reported no significant differences between them (artificial pupil diameters between 3.5 and 1.6 mm). The PureVision Multifocal is a centrenear aspheric simultaneous vision contact lens. Previous research 10,15 has shown that multifocal simultaneous vision contact lenses are an accepted good solution to contact lens correction of presbyopia. To the authors knowledge, the present study is the first to compare visual performances offered by contact lens-based artificial pupils and simultaneous contact lenses. The present study showed good results in terms of visual acuity for distance under photopic conditions, being 0.02 logmar or better for both systems; however, these values were lower under mesopic conditions. These photopic binocular distance visual acuity values agree with those previously reported in patients fitted with PureVision Multifocal contact lenses; 10,15 however, worse results were found by Gupta, Naroo and Wollfsohn 16 using the high addition PureVision Multifocal contact lens ( logmar). This might be due partly to the sample characteristics, as this study included patients with a maximum spectacle astigmatism of DC, whereas it was just 0.50 DC in the present study. Slight methodological differences and luminance conditions, only specified to be consistently of 500 lux, could also account for the differences to some extent. In our study, BDVA was also evaluated under mesopic conditions, obtaining values of logmar and for the pinhole system and PureVision Multifocal, respectively. This result with PureVision Multifocal is in agreement with the only study that has evaluated these multifocal contact lenses at this luminance level 15 and with previous studies that fitted other multifocal lenses, demonstrating the dependence of vision on pupil size, when wearing multifocal contact lenses and its compromise under low light levels. A pinhole contact lens provides functional intermediate vision, probably due to increased depth of focus (Figure 2 shows the visual acuity change with vergence from 6/12 to 6/6). It may be also observed from this figure that the PureVision Multifocal appeared to provide better binocular visual acuity at any vergence compared to the pinhole system, although no statistically significant differences were found (p > 0.05). Gupta, Naroo and Wollfsohn 16 reported a visual acuity of logmar at 80 cm, while in the present study values between 0.10 (Pure- Vision Multifocal) and 0.15 logmar (pinhole system) were found for the same distance. The two contact lens corrections in these studies provided poor levels of binocular near visual acuity, namely 0.19 logmar for the pinhole system and logmar for the PureVision Multifocal (Table 2), the latter being 50 Clinical and Experimental Optometry 2012 Optometrists Association Australia

6 significantly better (p < 0.05). Differences between the results obtained for each correction system are related to the age range of the sample (from 50 to 64 years), as the effect of depth of focus does not seem enough so provide clear close vision. Gupta, Naroo and Wollfsohn 16 obtained visual acuity values of logmar with high addition PureVision Multifocal contact lenses, similar to those reported here; however, these results do not agree with the findings of other studies with the same multifocal contact lenses 10,15 or with the SofLens Multifocal contact lens, 17 which has a similar design. The subjects examined in this study have two possible aperture stops, the natural pupil and the pinhole contact lens system fitted on the cornea and if the contact lens decentres, the effective pupil could be reduced in area and be defined by parts of the circumference of both stops. Considering the typical soft contact lens movement with blink, which is about 1.0 mm and the mean pupil diameter for near in these subjects ( mm), any possible displacement of the contact lens could never overlap the natural pupil and the visual axis will be cleared. In relation to a possible aperture decentration from the visual axis, which might occur with the contact lens pinhole, a more peripheral part of the cornea would be used to form the retinal image. These effects seem to be less important compared to the expected improvement in the depth-of-field produced by the pinhole system. The visual performance parameter that best identifies the limits of human spatial vision is the contrast sensitivity function, which plots the reciprocal of the contrast threshold as a function of the spatial frequency. Thus, to better gauge real-world visual function with the two types of presbyopic contact lenses, the binocular distance and near contrast sensitivities were measured in this study. Binocular distance contrast sensitivity revealed statistically significant differences between systems at six and 12 cycles per degree (p < 0.05) (Figure 3) and was significantly poorer with the pinhole contact lens under photopic and mesopic conditions. For near, no differences were found between the two presbyopic corrections for low spatial frequencies (p > 0.05) but the differences were statistically significant at six, 12 and 18 cycles per degree (p < 0.05). The present results agree with some other PureVision Multifocal studies. 15,16 Previous reports using other multifocal contact lens types reported variability among the contrast sensitivity results, possibly due to the sample characteristics, the fitting of the lens or the lens design. No previous studies have analysed the contrast sensitivity in patients with a contact lens-based artificial pupil. Therefore, a direct comparison with other reports is not possible. To analyse the effect of the unilateral character of the procedure on binocular vision, stereoacuity was assessed in these subjects. Stereopsis contributes to the perception of depth and distance and participates in the process of recognition of solid objects. Stereoscopic acuity is the ability to discriminate very fine differences in depth from geometric disparity. Good stereopsis for near is required for accurate hand-eye co-ordination. 27 Stereoacuity tests vary in practical aspects such as size and complexity of equipment, abilities of the patient and speed of application. Titmus and Random dot stereo tests provide fixed disparities and hence, accuracy of the outcomes depends on the number of steps and their disparity level. In contrast, the Howard Dolman method 28 gives a continuous measure of stereoacuity with high accuracy. The authors point out that using this method the stereoscopic threshold for each patient can be determined and the measure is more accurate than standard clinical stereotests. Stereopsis is affected by refractive blur 29 and reduced contrast sensitivity. 30 Values for a normal phakic population using the Howard Dolman method vary with age and a result of 14 seconds of arc or better is expected with a normal binocular system. 31 The mean values of stereoacuity obtained for the artificial pupil ( seconds of arc) were worse than for the PureVision Multifocal ( seconds of arc) (p < 0.01). These significant differences occur because the effects of monocular blur on stereoacuity are known to be greater than the effects of binocular blur (for example, superimposed retinal images in multifocal lenses). 32 Differences between the two systems agree with the differences obtained in terms of visual acuity and contrast sensitivity in near vision. The magnitude of stereoacuity observed in this study was greater (poorer stereoacuity) than that found in the only study investigating the same lenses using the Howard Dolman apparatus. 10 Previous reports 16,17,33,34 have used only vectographic tests to estimate local stereoacuity, such as the Titmus and Randot tests in centre-near aspheric simultaneous vision contact lenses. Our results show slightly worse values for stereoacuity than those reported by Richdale, Mitchell and Zadnik 17 ( seconds of arc) and much worse than those reported by Back, Grant and Hine 33 (92 51 seconds of arc) or Woods, Woods and Fonn 34 (54 35 seconds of arc) using the Randot test. Gupta, Naroo and Wollfsohn 16 obtained a higher stereoacuity value ( seconds of arc) with the TNO random dot stereogram. These differences may be due to the sample characteristics and especially to the use of different tests. The Howard Dolman apparatus accurately analyses the stereoscopic threshold in contrast to more commercial and clinically used vectographic tests. Disparity steps, interpupillary distance, working distance and monocular cues in vectographic tests influence the outcomes and caution should be exercised when using it. No previous studies have analysed the effect of artificial pupils on stereoacuity threshold. In conclusion, the results of the present study show that although there is an increase in depth-of-field of the eye due to the decreased aperture size, soft contact lenses with an aperture do not provide any improvement on the PureVision Multifocal contact lenses, offering significantly worse visual performance for near vision. GRANTS AND FINANCIAL ASSISTANCE This research was supported in part by a Ministerio de Ciencia e Innovación Clinical and Experimental Optometry 2012 Optometrists Association Australia 51

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